1. Field of the Invention
This invention relates to heat exchangers which are applicable to air conditioners particularly used for vehicles. In addition, this invention also relates to methods of manufacturing the heat exchangers.
This application is based on Patent Application No. Hei 11-153022 filed in Japan, the content of which is incorporated herein by reference.
2. Description of the Related Art
In general, heat-exchanger tubes are used for heat exchangers which are installed in air conditioners of vehicles, for example. The heat-exchanger tubes are mainly classified into two types of tubes (or pipes), which are shown in FIGS. 19 and 20 respectively.
FIG. 19 shows an example of a so-called xe2x80x9cseam welded tubexe2x80x9d, which is designated by a reference numeral xe2x80x9c1xe2x80x9d. That is, the seam welded tube 1 is constructed by a tube 2 having a flat shape and a corrugated inner fin 4. Herein, the corrugated inner fin 4 is inserted into the tube 2 by way of its opening 3. The corrugated inner fin 4 is formed in a corrugated shape having waves whose crest portions xe2x80x9c4axe2x80x9d are bonded to an interior surface of the tube 2 by welding, or the like.
FIG. 20 shows an example of an extrusion tube, which is designated by a reference numeral xe2x80x9c5xe2x80x9d. The extrusion tube 5 has tube portions xe2x80x9c6xe2x80x9d and partition walls xe2x80x9c7xe2x80x9d, which are integrally formed by extrusion molding.
If a heat exchanger is designed using the seam welded tube 1 shown in FIG. 19, it has an advantage in which since the corrugated inner fin 4 is inserted into the tube 2, an overall heating area is enlarged to improve a heat transfer rate. However, there is a disadvantage in which manufacturing such a heat exchanger needs much working time in insertion of the corrugated inner fin 4 into the tube 2 and welding of the corrugated inner fin 4 being bonded to the interior surface of the tube 2. This causes a problem in which the manufacturing costs are increased by the need for human effort.
If a heat exchanger is designed using the extrusion tube 5 shown in FIG. 20, it has an advantage in which, since the partition walls 7 are formed to partition an inside space of the extrusion tube 5 into multiple tube portions 6, an overall heating area is enlarged to improve a heat transfer rate. The extrusion tube 5 is manufactured using an extrusion molding technique. So, it is difficult to make the tube portions 6 sufficiently small, and it is difficult to make the thickness of the partition walls 7 sufficiently thin. In addition, the extrusion molding technique needs an increasing amount of materials used for formation of the extrusion tube 5, so that manufacturing costs are increased. Further, it is impossible to improve heat-exchange capability so much due to the relatively large thickness of the partition walls 7.
It is an object of the invention to provide a heat exchanger that is improved in pressure strength and heat-exchange capability without increasing manufacturing costs significantly.
It is another object of the invention to provide a method for manufacturing the heat exchanger.
A heat exchanger is constructed by tubes, corrugated fins and head pipes, which are assembled together. Herein, the tube is constructed by bending a flat plate whose surfaces are clad with brazing material to form a first wall and a second wall, which are arranged opposite to each other with a prescribed interval of distance therebetween to provide a refrigerant passage. Before bending, a number of swelling portions are formed by pressing to extend from an interior surface of the flat plate. By bending, the swelling portions are correspondingly paired in elevation between the first and second walls, so their top portions are brought into contact with each other to form columns each having a prescribed sectional shape corresponding to an elliptical shape or an elongated circular-shape each being defined by a short length and a long length. The columns are arranged to align long lengths thereof in a length direction of the tube corresponding to a refrigerant flow direction such that obliquely adjacent columns, which are arranged adjacent to each other obliquely with respect to the length direction of the tube, are arranged at different locations and are partly overlapped with each other with long lengths thereof in view of a width direction perpendicular to the length direction of the tube. The tubes, corrugated fins and head pipes are assembled together and are then placed into a heating furnace to heat for a prescribed time.
Because of the aforementioned arrangement and formation of the columns inside of the tube, it is possible to improve an overall heat transfer rate of the tube on the average, and it is possible to improve a pressure-proof strength with respect to the tube.
Incidentally, each of the columns has the prescribed sectional shape which is defined by a relationship of   2.0  ≤      d2    d1    ≤      3.0    .  
In addition, using a first center distance p1 being measured between the obliquely adjacent columns in the width direction of the tube and a second center distance p2 being measured between the obliquely adjacent columns in the length direction of the tube, the columns are arranged inside of the tube to meet relationships of   1.5  ≤      p1    d1    ≤      3.0    ⁢          xe2x80x83        ⁢    and    ⁢          xe2x80x83        ⁢    0.5    ≤      p2    d2    ≤      1.5    .  